Brushless DC motor coupled directly to AC source and electric apparatus using the same motor

ABSTRACT

A brushless DC motor is disclosed, in which a commercial AC source is full-wave rectified by a rectifier and then converted into a generally flat and low DC voltage not more than 45V by a DC voltage converter. The low DC voltage is applied in a full-wave driving method to a stator coil via an inverter circuit formed of switching elements in a bridge configuration. This structure allows obtaining the brushless DC motor coupled directly to the AC source, and the torque ripples and uneven rotation of the motor are suppressed.

This Application is a U.S. National Phase Application of PCTInternational Application PCT/JP2004/010982 dated Jul. 26, 2004.

TECHNICAL FIELD

The present invention relates to brushless DC motors for driving fans,and it also relates to electric apparatuses using the same motors.

BACKGROUND ART

Recently, a brushless DC motor employing permanent magnets has becomewidely used for driving a fan of a ventilator. FIG. 23 shows a circuitdiagram of a conventional brushless DC motor coupled directly to an ACsource to be used for driving a fan. The circuit uses the two-phasehalf-wave driving method and comprises the following elements:

-   -   rectifier 101 for rectifying the commercial AC power;    -   smoothing large capacity aluminum electrolytic capacitor 109;    -   two-phase stator coils 103, 104 for driving magnet rotor 105;        and    -   controller 102 for controlling the power to the stator coils,        including switching elements 107, 108 and being mounted on        printed circuit board 106. Stator coils 103, 104 are provided        with a high voltage DC power source directly from rectifier 101,        and controller 102 is provided with a low voltage reduced from        the high voltage DC power source. The foregoing brushless DC        motor driven by the two-phase half-wave driving method generates        rather large noises and vibrations, and needs a smoothing        capacitor of large capacity. The present invention aims to        provide a brushless DC motor coupled directly to the AC source        which overcomes those problems.

DISCLOSURE OF THE INVENTION

The brushless DC motor, coupled directly to the AC source, of thepresent invention comprises the following elements:

-   -   a stator including a stator coil;    -   a rotor including a rotor magnet;    -   a magnetic flux sensor for sensing a distribution of magnetic        flux density of the rotor magnet;    -   an inverter circuit including a plurality of switching elements        coupled in a full-wave bridge having an upper arm and a lower        arm;    -   an AC source coupler;    -   a rectifier for full-wave rectifying a voltage of the AC source;    -   a DC voltage converter for converting a rectified voltage        supplied from the rectifier into a flat low DC voltage, and for        applying the flat low DC voltage to the inverter circuit as a        power supply: and    -   a controller for controlling the inverter circuit based on a        signal supplied from the magnetic flux sensor such that the low        DC voltage is supplied to the stator coils in a full-wave        driving method.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a sectional view of a brushless DC motor in accordance witha first exemplary embodiment of the present invention.

FIG. 2 shows an electric circuit of the brushless DC motor shown in FIG.1.

FIG. 3 shows an output voltage waveform of a rectifier of the brushlessDC motor shown in FIG. 1.

FIG. 4 shows an electric circuit, using a PWM method, of the brushlessDC motor shown in FIG. 1.

FIG. 5 shows an electric circuit of a brushless DC motor in accordancewith a second exemplary embodiment of the present invention.

FIG. 6 shows the characteristics of rpm—torque of the brushless DC motorshown in FIG. 5.

FIG. 7 shows an electric circuit, using the PWM method, of the brushlessDC motor shown in FIG. 5.

FIG. 8 shows an electric circuit of a brushless DC motor in accordancewith a third exemplary embodiment of the present invention.

FIG. 9 shows the characteristics of rpm—current of the brushless DCmotor shown in FIG. 8.

FIG. 10 shows the characteristics of rpm—torque of the brushless DCmotor shown in FIG. 8.

FIG. 11 shows the characteristics of air volume—static pressure of aventilator using the brushless DC motor shown in FIG. 8.

FIG. 12 shows an electric circuit, using the PWM method, of thebrushless DC motor shown in FIG. 8.

FIG. 13 shows an electric circuit of a brushless DC motor in accordancewith a fourth exemplary embodiment of the present invention.

FIG. 14 shows the characteristics of rpm—torque of the brushless DCmotor shown in FIG. 13.

FIG. 15 shows the characteristics of air volume—static pressure of aventilator using the brushless DC motor shown in FIG. 13.

FIG. 16 shows an electric circuit, using the PWM method, of thebrushless DC motor shown in FIG. 13.

FIG. 17 shows an electric circuit of a brushless DC motor in accordancewith a fifth exemplary embodiment of the present invention.

FIG. 18 shows an electric circuit, using the PWM method, of thebrushless DC motor shown in FIG. 17.

FIG. 19 shows an electric circuit of a brushless DC motor in accordancewith a sixth exemplary embodiment of the present invention.

FIG. 20 shows an electric circuit of a brushless DC motor in accordancewith a seventh exemplary embodiment of the present invention.

FIG. 21 shows an electric circuit, using the PWM method, of thebrushless DC motor shown in FIG. 20.

FIG. 22 shows a lateral view, front view, and plan view of a ventilatorusing the brushless DC motor of the present invention.

FIG. 23 shows an electric circuit of a conventional brushless DC motor.

BEST MODE FOR PRACTICING THE INVENTION

Exemplary embodiments of the present invention are demonstratedhereinafter with reference to the accompanying drawings.

EXEMPLARY EMBODIMENT 1

FIG. 1 shows a sectional view of brushless DC motor 1 in accordance withthe first exemplary embodiment. Stator 10 is molded of thermosettingresin 17 such as unsaturated polyester. Stator iron core 10 a havingplural slots is wound with stator coils 2 via insulated material 11.Bracket 18 holds bearing 19, and magnet rotor 3 rotatably faces stator10.

Magnet rotor 3 is injection-molded of plastic magnet in one body withshaft 20 and provided with the polarity orientation when it is molded.Rotor magnetic pole 3 a is thus pole-anisotropic magnet.

Hall element 4 is used as a magnetic flux sensor which senses adistribution of magnetic flux density of the rotor magnetic pole 3 a. Aspace between hall element 4 and rotor magnetic pole 3 a is set suchthat the waveform of the distribution of the magnetic flux densitysensed by hall element 4 becomes a similar figure to the waveform of avoltage induced in stator coil 2 by rotor magnetic pole 3 a.

FIG. 2 shows the electric circuit of the brushless DC motor of thepresent embodiment. The commercial AC source is coupled to AC sourcecoupler 15, which has two terminals, namely, strong output terminal 15 aand weak output terminal 15 b, for obtaining rpm vs. torquecharacteristics in two steps. More terminals will produce more steps ofthe characteristics. Terminal 15 c is used as a common terminal. Outerswitch 24 selects one of terminal 15 a or terminal 15 b.

Rectifier 9 provides the commercial AC source with full waverectification. DC voltage converter 8 formed of step-down choppercircuits reduces a full-wave rectified high voltage supplied fromrectifier 9 to a low DC voltage of not more than 45V and outputs the lowDC voltage. This low DC voltage is applied to inverter circuit 6 as apower supply.

Smoothing capacitor 13 formed of polymer capacitor and having a smallcapacity is placed between rectifier 9 and DC voltage converter 8, sothat capacitor 13 complements a voltage in a rather short period, e.g.approx. 2.1 mil. sec, where AC 100V 50 Hz rectified in full-wavedecreases to not more than 45V (Refer to FIG. 3).

Connection sensor 16 senses which terminals 15 a or 15 b is selected byswitch 24. In the case of selecting weak output terminal 15 b, DCvoltage changer 14 reduces the low DC voltage supplied from converter 8lower than the one in the case of selecting strong output terminal 15 a.In FIG. 2, the circuit surrounded by alternate long and short dash linesis formed into one-chip IC 21 except the smoothing capacitor and coilsand being mounted on an aluminum substrate.

Magnetic flux density synthesizer 12 deducts phase-V waveform fromphase-U waveform of hall element 4 in order to remove harmonics ofphase-U current of the motor. Synthesizer 12 also deducts phase-Wwaveform from phase-V waveform of hall element in order to remove theharmonics of phase-V current of the motor. Synthesizer 12 deductsphase-u waveform from phase-W waveform of hall element 4 in order toremove the harmonics of phase-w current of the motor.

Switching elements Q1, Q3, Q5 disposed in the upper arm and switchingelements Q2, Q4, Q6 disposed in the lower arm are coupled together in afull-wave bridge, thereby forming inverter circuit 6.

Controller 5 controls inverter circuit 6 based on signals supplied fromhall elements 4 such that stator coils 2 can be full-wave driven along agiven direction and in a given sequence.

Current waveform controller 7 adjusts an output bias current so as toshape a waveform of the motor current into a similar figure with thewaveform from which the harmonics have been removed by synthesizer 12while providing switching elements Q1-Q6 with feedback in order to keepthe switching elements in an unsaturated state yet close to a saturatedstate.

In the brushless DC motor of the present invention, DC voltage converter8 converts a high voltage undergone the full-wave rectification into apredetermined low DC voltage not more than 45V and supplies this low DCvoltage to stator coil 2. A voltage fluctuation in the AC source thusdoes not change the characteristics of the motor. The motor is poweredby full-wave driving of the inverter circuit 6 at a generally flat lowDC voltage, and yet, harmonics of the motor current are removed, so thatthe motor produces fewer noises and vibrations. As shown in FIG. 3,smoothing capacitor 13 can have a small capacity just enough forcomplementing the voltage in a rather short period, e.g. approx. 2.1mil. sec. where the voltage becomes insufficient. Smoothing capacitor 13thus can employ a smaller capacitor, e.g. a solid-state capacitorfeaturing a longer life and fewer changes in the characteristics due toambient temperatures. The solid-state capacitor includes a polymercapacitor, ceramic capacitor, and film capacitor.

As shown in FIG. 4, the pulse width modulation (PWM) control isapplicable to the brushless DC motor of the present embodiment. PWMcontroller 25 controls switching elements Q2, Q4, and Q6 of the lowerarm in PWM method, and also controls inverter circuit 6 based on signalssupplied form hall element 4 such that power is supplied in full-wavedriving to stator coils 2 in a given direction and sequence. Currentwaveform controller 7 adjusts an ON/OFF duty of the switching elementsdisposed in the lower arm for controlling the waveform. Switchingelements Q1, Q3, and Q5 of the upper arm can be PWM-controlled insteadof the switching elements of the lower arm. As a result, the number ofsteps for adjusting the specification of the apparatus can be reduced.

Duty instruction means 26 gives an instruction for the ON/OFF duty ofPWM with a voltage reduced from the low DC voltage.

Coupling sensor 16 senses which terminal 15 a or 15 b of AC sourcecoupler 15 is selected by switch 24. When weak output terminal 15 b isselected, duty instruction means 26 shortens an ON duty of PWM so thatan average voltage applied to stator coils 2 becomes lower than thatwhen strong output terminal 15 a is selected.

EXEMPLARY EMBODIMENT 2

FIG. 5 shows an electric circuit of the brushless DC motor in accordancewith the second exemplary embodiment of the present invention. Elementssimilar to those in the previous embodiment have the same referencemarks and the descriptions thereof are omitted here.

Current sensor 30 senses a current of inverter circuit 6. Currentcontroller 31 adjusts the low DC voltage supplied from DC voltageconverter 8 such that an average current of inverter circuit 6 becomesequal to the set current. An upper limit voltage is set to the low DCvoltage to be applied to inverter circuit 6 because a withstandingvoltage and a kick-back voltage of the switching elements should betaken into consideration.

Coupling sensor 16 senses which terminal 15 a or 15 b of AC sourcecoupler 15 is selected by switch 24. When weak output terminal 15 b isselected, coupling sensor 16 instructs set-current changer 32 to lowerthe set current of inverter circuit 6 than that of when strong outputterminal 15 a is selected.

In the brushless DC motor of the present embodiment, the average currentof inverter circuit 6 is kept constant, so that output torque isgenerally kept constant as shown in FIG. 6. Since a difference in rpmwith respect to a change in load is thus great, the ventilator employingthe brushless DC motor of the present embodiment has the characteristicsof air volume vs. static pressure similar to that of the ventilatoremploying an induction motor. The foregoing structure thus allowspreventing an extreme low static pressure or an extreme large air volumeat 0 (zero) static pressure, and also obtaining a ventilator of lownoise and low power consumption.

FIG. 7 tells that the PWM control is applicable to the brushless DCmotor of the present embodiment as described in the previous embodiment.Current controller 31 controls duty instruction means 26 for adjustingan ON/OFF duty of the PWM such that the average current of invertercircuit 6 becomes equal to the set current. In other words, the low DCvoltage supplied from DC voltage converter 8 is adjusted.

EXEMPLARY EMBODIMENT 3

FIG. 8 shows an electric circuit of the brushless DC motor in accordancewith the third exemplary embodiment of the present invention. Elementssimilar to those in the previous embodiment have the same referencemarks and the descriptions thereof are omitted here.

Rotary signal output means 34 outputs pulses indicating an rpm of themotor from the waveform sensed by magnetic flux sensor 4. Currentinstructing means 33 converts this pulse waveform from frequency tovoltage and obtains a voltage, namely, an rpm of the motor. In responseto the rpm of the motor, current instructing means 33 instructs invertercircuit 6 to increase a current with reference to the set value. Inother words, current instructing means 33 gives an instruction tocircuit 6 to increase the current at the greater rpm.

Current controller 31 adjusts the low DC voltage supplied from DCvoltage converter 8 such that an average current of inverter circuit 6becomes equal to the current designated by current instructing means 33.An upper limit voltage is set to the low DC voltage to be applied toinverter circuit 6 because a withstanding voltage and a kick-backvoltage of the switching elements should be taken into consideration. Asa result, within a certain period, the motor can operate at a constantvoltage without controlling the current even the rpm rises.

Coupling sensor 16 senses which terminal 15 a or 15 b of AC sourcecoupler 15 is selected by switch 24. When weak output terminal 15 b isselected, coupling sensor 16 instructs set-current changer 32 to lowerthe set current of inverter circuit 6 than that of when strong outputterminal 15 a is selected.

In the brushless DC motor of the present embodiment, an increment of therpm increases the current of inverter circuit 6 as shown in FIG. 9, andthe torque increases as shown in FIG. 10. In other words, currentinstructing means 33 increases the current of inverter circuit 6 inresponse to an increment of the rpm of the motor so that the torquecurve can get a desirable gradient.

The ventilator employing the brushless DC motor of the presentembodiment can thus obtain the characteristics of air volume vs. staticpressure, as shown in FIG. 11. The characteristics get the air volumechanges only extremely few even if a pressure loss changes by the outerwind pressure or by the difference of the duct length.

FIG. 12 tells that the PWM control is applicable to the brushless DCmotor of the present embodiment as described in the previous embodiment.Current controller 31 controls duty instruction means 26, therebyadjusting the ON/OFF duty of the PWM such that the average current ofinverter circuit 6 becomes equal to the current instructed by currentinstructing means 33 to change in response to the rpm of the motor.

An upper limit of the current of inverter circuit 6 is set consideringthe allowable power consumption of inverter circuit 6. The ON duty ofPWM is set 100% at the upper limit so that a rise of the rpm will notaccompany an increment of the current, and the motor operates at ON dutyof 100% in a certain period.

EXEMPLARY EMBODIMENT 4

FIG. 13 shows an electric circuit of the brushless DC motor inaccordance with the fourth exemplary embodiment of the presentinvention. Elements similar to those in the previous embodiment have thesame reference marks and the descriptions thereof are omitted here.

Rotary signal output means 34 outputs pulses indicating an rpm of themotor from the waveform sensed by magnetic flux sensor 4. Rpm rangesensor 39 converts this pulse waveform from frequency to voltage andobtains an rpm range including the rpm of the motor at that time (Referto FIG. 14).

Current instructing means 40 instructs inverter circuit 6 to change thecurrent in response to the rpm range. To be more specific, currentinstructing means 40 gives an instruction to inverter circuit 6 suchthat a greater rpm accompanies an increment of the current step by stepcorresponding to each one of the rpm ranges.

Current sensor 30 senses a current of inverter circuit 6. Currentcontroller 31 adjusts the low DC voltage supplied from DC voltageconverter 8 such that an average current of inverter circuit 6 becomesequal to the current designated by current instructing means 40. Anupper limit voltage is set to the low DC voltage to be applied toinverter circuit 6 because a withstanding voltage and a kick-backvoltage of switching elements Q1-Q6 should be taken into consideration.As a result, within a certain period, the motor can operate at aconstant voltage without controlling the current even if the rpm rises.

Coupling sensor 16 senses which terminal 15 a or 15 b of AC sourcecoupler 15 is selected by switch 24. When weak output terminal 15 b isselected, coupling sensor 16 instructs set-current changer 32 to lowerthe set current of inverter circuit 16 than that of when strong outputterminal 15 a is selected.

As shown in FIG. 14, in the brushless DC motor of the presentembodiment, the torque increases step by step at the greater rpm of themotor. In other words, current instructing means 40 increases thecurrent of inverter circuit 6 step by step in response to an incrementof the rpm of the motor so that the torque curve can get a desirablegradient. At the broken lines of torque characteristics shown in FIG.14, hysteresis between fall and rise of the rpm is set, and a width ofthe hysteresis is set appropriately not to invite inconvenience, e.g.hunting. The stepwise change of the current permits a frequency-voltageconverter having a smaller dynamic range to be usable.

The ventilator employing the brushless DC motor of the presentembodiment has the characteristics of air volume vs. static pressure, asshown in FIG. 15. The characteristics get the air volume changes onlyextremely few even if a pressure loss changes by the outer wind pressureor by the difference of the duct length.

FIG. 16 tells that the PWM control is applicable to the brushless DCmotor of the present embodiment as described in the previous embodiment.Current controller 31 controls duty instruction means 26, therebyadjusting the ON/OFF duty of the PWM such that the average current ofinverter circuit 6 becomes equal to the current instructed by currentinstructing means 33 to change in response to the rpm range of themotor. An upper limit to the current of inverter circuit 6 is neededbecause of the same reason as described in the previous embodiment.

EXEMPLARY EMBODIMENT 5

FIG. 17 shows an electric circuit of the brushless DC motor inaccordance with the fifth exemplary embodiment of the present invention.Elements similar to those in the previous embodiment have the samereference marks and the descriptions thereof are omitted here.

Voltage reducing means 46 is placed outside the motor via terminals 44ant 45. The low DC voltage supplied from DC voltage converter 8 isapplied to inverter circuit 6 via voltage reducing means 46.

The foregoing structure allows obtaining a brushless DC motor directlycoupled to the AC source, and the motor can be adjusted its speedsmoothly, i.e. not the step-like adjustment, so that a ventilator can beset its air volume arbitrarily. FIG. 18 tells that the PWM control isapplicable to the brushless DC motor of the present embodiment asdiscussed in the previous embodiment.

EXEMPLARY EMBODIMENT 6

FIG. 19 shows an electric circuit of the brushless DC motor inaccordance with the sixth exemplary embodiment of the present invention.Elements similar to those in the previous embodiment have the samereference marks and the descriptions thereof are omitted here.

Voltage reducing means 46 is placed outside the motor via terminals 53and 54. PWM controller 25 controls switching elements Q2, Q4, and Q6disposed in the lower arm. Current waveform controller 51 adjusts anON/OFF duty of the switching elements of the lower arm such that awaveform of the motor current becomes a similar figure to the waveformfrom which the harmonics have been removed by magnetic flux densitysynthesizer 12. Reference voltage generating circuit 52 reduces the lowDC voltage supplied from a DC voltage converter 50, thereby generating areference voltage of constant output. The reference voltage is then, viavoltage reducing means 46 outside the motor, applied to PWM controller25 as a duty instruction voltage indicating an ON/OFF duty of the PWM.

The foregoing structure allows obtaining a brushless DC motor directlycoupled to the AC source, and the motor can be adjusted its speedsmoothly, i.e. not the step-like adjustment, so that the ventilator canbe set its air volume arbitrarily.

EXEMPLARY EMBODIMENT 7

FIG. 20 shows an electric circuit of the brushless DC motor inaccordance with the seventh exemplary embodiment of the presentinvention. Elements similar to those in the previous embodiment have thesame reference marks and the descriptions thereof are omitted here.

Voltage reducing means 46 is placed outside the motor via terminals 53and 57. Reference voltage generating circuit 52 reduces the low DCvoltage supplied from DC voltage converter 8, thereby generating areference voltage of constant output. The reference voltage is then, viavoltage reducing means 46 outside the motor, applied to set currentchanger 32.

Set current changer 32 changes the reference value depending on avoltage applied. Current instructing means 33 instructs inverter circuit6 in response to an output signal supplied from rotary signal outputmeans 34 to run a constant current, or change the current with respectto the reference value, or change the current stepwise with respect tothe reference value. At this time, an upper limit voltage is set to thelow DC voltage to be applied to inverter circuit 6 because awithstanding voltage and a kick-back voltage of the switching elementsshould be taken into consideration. As a result, within a certainperiod, the motor can operate at a constant voltage without controllingthe current even if the rpm rises.

In this embodiment, the current of inverter circuit 6 increases at agreater rpm, and on the contrary, decreases at a smaller rpm. As aresult, the shaft torque of the motor increases at the greater rpm. Theventilator employing the brushless DC motor of this embodiment obtainsthe characteristics of air volume changes only extremely few even if apressure loss changes by the outer wind pressure or by the difference ofthe duct length. FIG. 21 tells that the PWM control is applicable to thebrushless DC motor of this embodiment as discussed in the previousembodiment.

An electric apparatus employing the brushless DC motor of the presentinvention is demonstrated hereinafter. The brushless DC motor issuitable for electric apparatuses such as a ventilator and a blower.FIG. 22 shows a front view, side view, and plan view of the ventilatoremploying the brushless DC motor of the present invention.

In FIG. 22, ventilator 59 includes brushless DC motor 58 and centrifugalblower 60, where motor 58 rotates a sirocco fan of blower 60 forblowing. The motors discussed in the previous embodiments can be used asmotor 58, so that the ventilator of the present invention enjoys theadvantages of the motors.

The brushless DC motor directly coupled to the AC source of the presentinvention allows reducing torque ripples and reducing change rate ofmomentary torque, thereby suppressing noises and vibrations. This motorhas the following advantages: a small current; a wide range of loadtorque available; low power consumption at a high power output range; adownsized circuit; high quality; a long service life; suppressing unevenrotation; no changes in the characteristics upon a change in powersupply voltage; and equivalent rpm vs. torque characteristics to thoseof the induction motor. Further, this motor allows reducing the numberof steps of adjusting its specifications, so that it is useful to mountthis motor in electric apparatuses incorporating an centrifugal blower,such as a ventilator, water heater, air conditioner, air cleaner,dehumidifier, dryer, and fan-filter unit. Still further, since thismotor has the characteristics of rpm vs. torque, such that the shafttorque increases at a greater rpm, it is useful to mount this motor tothe following electric apparatuses which incorporate the centrifugalblower and require the characteristics of air volume vs. staticpressure, where almost no changes in air volume occur upon a change instatic pressure: a ventilator, water heater, air cleaner,air-conditioner, and a blower unit for a clean-room.

INDUSTRIAL APPLICABILITY

The brushless DC motor of the present invention is suitable for beingmounted in a ventilator and a blower.

1. A brushless DC motor coupled directly to an AC source, the motorcomprising: (a) a stator including a stator coil; (b) a rotor includinga rotor magnet; (c) a magnetic flux sensor for sensing magnetic-flux ofthe rotor magnet; (d) an inverter circuit including a plurality ofswitching elements coupled in a full-wave bridge having an upper arm anda lower arm; (e) a plurality of AC source couplers; (f) a rectifier forfull-wave rectifying a voltage of the AC source; (g) a DC voltageconverter for converting a rectified voltage supplied from the rectifierinto a low DC voltage, and for applying the low DC voltage to theinverter circuit as a power supply; (h) a controller for controlling theinverter circuit based on a signal supplied from the magnetic fluxsensor such that the low DC voltage is supplied to the stator coil in afull-wave driving method; and (i) a current controller for regulating anaverage current value applied to the inverter circuit constantly at aset current; (j) a set current changer for changing the set currentregulated by the current controller; wherein the set current changerchanges the set current regulated by the current controller in responseto which terminals of the AC source couplers are coupled to the ACsource.
 2. The brushless DC motor of claim 1 further comprising: acurrent instructing means for instructing an average current value tothe inverter circuit; and a terminal for connecting a voltage reducingmeans disposed outside the motor, wherein a signal voltage whichinstructs the average current value to the inverter circuit is appliedto the current instructing means via the voltage reducing means disposedoutside the motor and wherein the signal voltage instructs the invertercircuit to run a constant current.
 3. An electric apparatus in which thebrushless DC motor as defined in claim 1 is mounted.
 4. A brushless DCmotor coupled directly to an AC source, the motor comprising: (a) astator including a stator coil; (b) a rotor including a rotor magnet;(c) a magnetic flux sensor for sensing magnetic-flux of the rotormagnet; (d) an inverter circuit including a plurality of switchingelements coupled in a full-wave bridge having an upper arm and a lowerarm; (e) an AC source coupler; (f) a rectifier for full-wave rectifyinga voltage of the AC source; (g) a DC voltage converter for converting arectified voltage supplied from the rectifier into a low DC voltage, andfor applying the low DC voltage to the inverter circuit as a powersupply; (h) a controller for controlling the inverter circuit based on asignal supplied from the magnetic flux sensor such that the low DCvoltage is supplied to the stator coil in a full-wave driving method;(i) a current instructing means for instructing the average currentvalue for supplying to the inverter circuit; (j) a current controllerfor regulating the average current value supplied to the invertercircuit constantly at a instructed value; and (k) an output means foroutputting a signal of a motor rpm based on a signal supplied from themagnetic flux sensor; wherein the current instructing means instructsthe average current value for supplying to the inverter circuit inresponse to the motor rpm.
 5. The brushless DC motor of claim 4, whereinthe AC source coupler includes a plurality of terminals, wherein thecurrent instructing means changes an instruction of the average currentvalue in response to the motor rpm depending on which terminals of theAC source coupler are coupled to the AC source.
 6. The brushless DCmotor of claim 4, further comprising: a detecting means for detecting arpm range of the motor within which the motor rpm is included, whereinthe current instructing means instructs the average current value forsupplying to the inverter circuit in response to the rpm range of themotor.
 7. The brushless DC motor of claim 6 further comprising: aterminal for connecting a voltage reducing means disposed outside themotor, wherein a signal voltage which instructs the average currentvalue to the inverter circuit is applied to the current instructingmeans via the voltage reducing means disposed outside the motor andwherein the signal voltage instructs the inverter circuit to change acurrent in response to the rpm range of the motor.
 8. The brushless DCmotor of claim 4 further comprising: a terminal for connecting a voltagereducing means disposed outside the motor, wherein a signal voltagewhich instructs the average current value to the inverter circuit isapplied to the current instructing means via the voltage reducing meansdisposed outside the motor and wherein the signal voltage instructs theinverter circuit to change a current in response to the motor rpm.
 9. Anelectric apparatus in which the brushless DC motor as defined in claim 4is mounted.